center/back bracing is often not needed since the floor of the overflow (siliconed to the outside back or... inside, as the case here) is an incredible reinforcement. It's something like trying to bend a two by four timber by the narrow side versus the wide side... or the like old bar trick about trying to crush an egg between your fingers along its longest plane. Much stronger lengthwise.
That perpendicular floor is itself a very strong brace.
Looking at it another way/analogy: imagine typical top, euro-bracing... but lower (vis a vis, the overflow floor again here)
That all said... the aquarium in the image above looks to be made of (too) thin glass. The front will bow and perhaps bow too much to be safe. I'm very concerned about the front face and overall size/width of this tank being open topped. Do check with an engineer, but my recollection for common plate glass is that deflection (the "bow" here) should not exceed 1/2 the thickness of the glass. There is even less tolerance for white glass (ala Starfire, Diamante, etc).
So... a max "bow" of 1/4" on a 1/2" tank wall is acceptable. Yet this tank does not look to even be 1/2" thick by the image. And if so... may well be weakly contstructed. I'd at least like to see thicker walls if not additional bracing (1/2" Euro plates could go inside the front top face perhaps)
The caveat here... we are judging by image work. Not worth much (my advice

)
Above all heed the mfg advice/warranty and an engineers data on proper specs if possible.
kindly, Anthony